Method for accelerating insulation resistance measurement in an ungrounded power supply system

Description

[0001] The invention relates to methods for accelerating insulation resistance measurement for use in a method for determining insulation resistance using a pulse measurement method in an unearthed power supply system (IT system) according to the respective preambles in claims 1 and 8.

[0002] The application in both variants of the method according to the invention requires an existing, higher-level method for insulation monitoring, in which, according to a pulse measuring method, a measuring voltage composed of temporally successive rectangular measuring pulses is applied between at least one active conductor of the unearthed power supply system and earth by means of a measuring pulse generator via a coupling branch with a coupling resistor and a measuring resistor, and a time-continuous curve of a voltage measured across the measuring resistor is recorded.

[0003] In addition to the use of the methods according to the invention for stationary ungrounded power supply systems, for example in industrial plants or hospitals, electromobility in particular deserves special attention with regard to electrical safety.

[0004] In the automotive sector, monitoring the insulation resistance of the ungrounded power supply system is becoming increasingly important, since the power supply system in the electric vehicle is an isolated power supply system and the insulation resistance is an important indicator of the quality status of the on-board electrical installation.

[0005] Insulation monitoring devices are therefore used to continuously monitor insulation resistance. The LV 123 test standard specifies test conditions for testing high-voltage components for electric vehicles. Two measurement modes are distinguished for insulation resistance measurement: LV123-639 for normal operation and LV123-1735 for quick-start mode.

[0006] The LV123-639 standard states that the time until a valid insulation resistance value is output must be less than 30 s, unless the original equipment manufacturer's requirements documentation contains other information.

[0007] If fast insulation monitoring is required, the LV123-1735 standard requires that the time until a valid insulation resistance value is output must be less than 5s and that a measurement tolerance of 0% to -50% in the range from 100 Ohm / V to 500 Ohm / V must be maintained.

[0008] In addition, the additional standard LV123-1734 specifies that the time until a valid insulation resistance value is output must be specified by the original equipment manufacturer depending on the values ​​of leakage capacitances and Y capacitors up to 2µF and depending on the high-voltage potential.

[0009] A quick start for insulation resistance measurements is also important in conjunction with the DIN EN 61557-8 standard, which specifies the requirements for insulation monitoring devices for IT systems. For example, in conjunction with insulation monitoring in an electric vehicle, it would seem sensible for the driver to receive a message after starting the electrical system that the insulation status of the on-board electrical system is "safe" or is assessed as "unsafe" in the form of a warning or error message.

[0010] The quick-start requirement of providing an insulation resistance value within 5 seconds cannot always be met, as the leakage capacitances of the IT network (electric vehicle's electrical system) and the Y capacitors of a load often still exhibit a residual voltage due to the charge transfer with the measurement pulse of a previous measurement cycle, even when insulation monitoring is performed using the pulse measurement method. A premature statement about the insulation condition, i.e., determined during the charging (re)charging process, in particular whether the quick-start requirement is met, is currently not possible according to the state of the art, as all methods are based on information that is only available after the charging (re)charging processes have been completed.

[0011] From the prior art, patent DE 10 2021 101 693 B3, in conjunction with a pulse measurement method for insulation monitoring, discloses a method for measuring pulse fault detection. This method involves a continuous calculation of time constants, from which an indication of the reliability of the insulation resistance measurement is derived. No statement is made as to whether the quick start requirement can be met.

[0012] The present invention is therefore based on the object of proposing a method with which, in conjunction with a pulse measuring method for insulation monitoring, a statement about the insulation condition can be made as early as possible, in particular whether the requirement of providing an insulation resistance value can be met within a predetermined quick start time.

[0013] This object is achieved in conjunction with the features in the preamble of claim 1 by specifying a target state of charge of the network capacities present in the ungrounded power supply system, calculating a target time at which the network capacities will have reached the target state of charge from the target state of charge (r) and the effective tau value,

[0014] Calculating a first waiting time starting from the current time as the difference between the target time and the current time and outputting a safe start signal if the first waiting time is less than a predetermined quick start time, otherwise outputting a non-safe start signal.

[0015] The considerations are based on state-of-the-art measurement methods for insulation monitoring that use a clocked measurement voltage. In this method, the measurement pulse generator of the insulation monitoring device (insulation monitoring device) uses the pulse measurement method to feed a measurement voltage composed of chronologically successive rectangular measurement pulses between at least one active conductor of the power supply system and earth (the chassis of the electric vehicle). A current flows through the insulation resistance in this measurement circuit, causing a proportional voltage drop across a measurement resistor. A measurement of this voltage (measured voltage) thus provides information about the magnitude of the insulation resistance and thus about the insulation condition of the (automotive) ungrounded power supply system.

[0016] Since the ungrounded power supply system has unavoidable electrical capacitances (system leakage capacitances) to earth and Y capacitors of the consumers for interference suppression, the accuracy and especially the speed of the insulation resistance measurement are negatively affected.

[0017] In the following, the system leakage capacitances and Y-capacitors are summarized under the term system capacitances and this capacitive arrangement is simply referred to as a capacitor.

[0018] By considering the capacitance-charging e-function (natural exponential function) and the time constants derived from it, which are influenced by the internal resistance of the insulation monitoring device, the insulation resistance and the network capacitances (RC element), important information about the insulation state can be obtained during the charging or discharging of the network capacitances, especially when starting up a mobile on-board network.

[0019] In a first process step, a sequence of time-discrete output voltage measured values ​​is generated from the (time-continuous) curve of the measured voltage by means of digital signal processing, which are then stored for further calculations.

[0020] In the following calculations, the mathematical principles that apply to the derivation rules of the e-function are applied to the technical facts of the capacitance-charging e-function, which describes the voltage curve during the charging of the network capacitances in the ungrounded power system.

[0021] The starting point of the considerations is therefore the relationship - here simplified with time-continuous quantities of a voltage curve V (t) (capacitor voltage) for a general RC element V ′ t V " t = − RC = − tau with V t = V 0 ∗ 1 − e − t RC during loading and V t = V 0 ∗ e − t RC during discharge, where V'(t), V"(t) are first and second time-continuous derivatives (differential quotients) of V(t).

[0022] For digital signal processing of the discrete-time measured values, the continuous-time derivatives are converted into first- and second-order difference quotients. The discrete-time output voltage measured values ​​and their first- and second-order difference quotients thus serve as the starting point for the subsequent calculation of time constants.

[0023] The time constants result as a negative quotient of a first-order difference quotient and a second-order difference quotient of temporally successive time-discrete output voltage measured values ​​in a calculation period that lies within a transient phase of the rectangular measuring pulse.

[0024] The calculation period in which the calculation of the time constant is continuously applied to the time-discrete output voltage measured values ​​extends within the transient phase of the rectangular measuring pulse from the time of the end of the transient process of the low-pass filter to the beginning of the saturation phase of the time-discrete output voltage measured values.

[0025] Using a single-stage or multi-stage time constant averaging, an effective tau value is calculated from the time constants thus formed as a final time constant available for further calculations, which is used as a fundamental value in the test of whether the fast start condition can be met.

[0026] In a first variant of the method according to the invention, a predefined target state of charge for the grid capacitances present in the ungrounded power supply system serves as the input parameter. This target state of charge defines the ratio of the target charging voltage achieved in this target state of charge to a steady-state final value (full charging voltage) of the voltage across the grid capacitances (capacitor voltage). Therefore, a (percentage) target value must be known that reflects a sufficiently steady-state state of charge of the capacitors that is valid for the insulation resistance measurement and is specified as a percentage based on a full charging voltage of the capacitors. For example, 99% of the full charging voltage (target state of charge 0.99) should be achieved in order to then be able to check whether this target state of charge can be achieved within a predefined quick-start time.

[0027] Using the target state of charge and the effective tau value, the target time can be determined and from this an initial waiting time can be calculated starting from the current time as the difference between the target time and the current time.

[0028] Finally, a safe start signal (ss) is output if the first waiting time (dTr) is less than a specified quick start time (Ts), otherwise a non-safe start signal (ns) is output.

[0029] In a further embodiment, the time-discrete output voltage measured values ​​are formed by generating a sequence of time-discrete input voltage measured values ​​by sampling the curve of the measured voltage at a predetermined sampling rate, calculating the time-discrete output voltage measured values ​​from the time-discrete input voltage measured values ​​by measuring the mean value with sampling rate reduction and calculating filtered voltage measured values ​​by digital low-pass filtering of decimated voltage measured values.

[0030] By means of digital signal processing methods, after sampling the curve of the measured voltage, the time-discrete input voltage measured values ​​are transformed via decimated voltage measured values ​​and filtered voltage measured values ​​into the time-discrete output voltage measured values.

[0031] The measured value averaging can be carried out in several stages, with a simultaneous reduction in the sampling rate.

[0032] On the one hand, this can significantly reduce the noise components that distort the measurement, and on the other hand, by continuously summarizing the time-discrete input voltage measured values ​​to an average value, the number of samples to be further processed per unit of time is reduced, which corresponds to the reduction in the sampling rate and thus places lower demands on the computing power and memory requirements for the execution of subsequent signal processing algorithms.

[0033] Advantageously, the measured value averaging comprises a first averaging, wherein the decimated voltage measured values ​​are formed consecutively over a number N of the time-discrete input voltage measured values ​​without overlap.

[0034] In this process, N discrete-time input voltage measurements are used consecutively, block by block and without block overlap, to calculate a linear average valid for the respective block. The combination of the N discrete-time input voltage measurements results in a sequence of decimated voltage measurements that represent the respective average and exhibit a significantly reduced noise component.

[0035] Furthermore, the measured value averaging comprises a second averaging, wherein the time-discrete output voltage measured values ​​are formed consecutively over a number M of the filtered voltage measured values ​​without overlap, and the number M is adaptively adapted to the time behavior of the time-discrete output voltage measured values ​​(Vi).

[0036] Thus, a further block-wise linear averaging of consecutive filtered voltage measurement values ​​without overlapping takes place, whereby, however, in comparison to the first averaging, the number M of the block-wise combined filtered voltage measurement values ​​can be adaptively adapted to the temporal course of the time-discrete output voltage measurement values.

[0037] In order to reduce the computational effort and still obtain the most accurate digital representation of the capacitance-charging voltage curve, a shorter block length is selected, for example, in the case of a rapid temporal change in the time-discrete output voltage measured values, i.e. a smaller number M of filtered voltage measured values ​​are combined to form a linear average, than in the case of a small temporal change in the time-discrete output voltage measured values.

[0038] Preferably, the adaptive adjustment is carried out by a first control which sets the number M as a function of the second-order difference quotient (V" i ) of the time-discrete output voltage measured values ​​(V i ) such that the second-order difference quotient (V" i ) of the time-discrete output voltage measured values ​​(V i ) lies within a permissible first value range.

[0039] The second-order difference quotient of the time-discrete output voltage measured values ​​is used as a benchmark and adjustment criterion in order to adapt the time behavior of the time-discrete output voltage measured values ​​as accurately as possible to the true time course of the measured voltage.

[0040] For the second-order difference quotient of the discrete-time output voltage measured values, a permissible first value range is defined within which this difference quotient may vary. Using feedback in the first control system, the second-order difference quotient calculated based on the discrete-time output voltage measured values ​​is fed back and evaluated. The number M of filtered voltage measured values ​​to be combined in blocks is set such that this difference quotient lies within the permissible first value range.

[0041] Advantageously, to calculate the effective tau value, a nested tau mean value and a second-order tau difference quotient are continuously calculated from three nested time constants, wherein a second control is carried out which sets the number M as a function of the second-order tau difference quotient such that the second-order tau difference quotient lies within a permissible second value range, and then an averaging is carried out over a number K of the nested tau mean values ​​to calculate the effective tau value.

[0042] Furthermore, a stationary final value (full charge voltage) of the capacitor voltage can be calculated from one of the stored, time-discrete voltage measurement values, the respective corresponding time and the effective tau value to Vstat = Vi / 1 − e − ti / tau _ eff

[0043] The object underlying the invention is also achieved in conjunction with the features in the preamble of claim 8 by specifying a target charging speed which is to be achieved at a target time at the network capacities present in the unearthed power supply system, calculating a second waiting time starting from the T2 time (t=T2) as the difference between the target time and the T2 time from the effective tau value and the quotient of the target charging speed and the determined first-order difference quotient at the T2 time and outputting a safe start signal if the second waiting time is less than a predetermined quick start time, otherwise outputting a non-safe start signal.

[0044] Including the method step of calculating the effective tau value, the second variant of the method according to the invention according to claim 8 corresponds to the initial method steps of the first variant according to claim 1.

[0045] In the second variant, as an alternative to the first variant, the input parameter is not the target state of charge, but rather a target charging rate, which reflects a sufficiently steady state of charge of the capacitors that is valid for the insulation resistance measurement. The target charging rate corresponds to the first-order difference quotient of the target charging voltage and is thus linked to the target time. Knowing the already determined and stored first-order difference quotient at time T2 (t=T2), a time difference from the stored T2 time is calculated as the second waiting time.

[0046] The further embodiments in the claims directly or indirectly referring back to the second variant according to claim 8 also correspond to the statements applicable to the first variant.

[0047] The idea underlying the method according to the invention in its first and second variants is thus to be able to advantageously predict a valid state of charge for calculating the insulation resistance, described, for example, by charging parameters such as the charging time or the full charging voltage, based on the ongoing charging or discharging process – in contrast to methods known from the prior art, in which the charging parameters are only known once the charging / discharging process has actually been completed. Thus, with the waiting times calculated according to the invention, it is no longer necessary for an evaluation unit (controller) to constantly query the AD converter in an energy-intensive manner to determine the current state of charge.

[0048] Further advantageous design features will become apparent from the following description and the drawings, which illustrate a preferred embodiment of the invention using examples. They show: Fig. 1: the determination of an insulation resistance in an unearthed power supply system according to the state of the art, Fig. 2A, 2B: an equivalent circuit diagram for charging / discharging a capacitor, Fig. 3A, 3B: a time curve of a capacitor voltage during charging / discharging of the capacitor, Fig. 4: First and second order differential quotients of the voltage curve according to Fig. 3A , Fig. 5: a negative time constant as a quotient of the differential quotients according to Fig. 4 , Fig. 6: a flow chart of the method according to the invention with specification of a target charge state (first variant), Fig. 7: a flowchart of the method according to the invention with specification of a target charging speed (second variant), Fig. 8: a flow chart for forming and storing the output voltage measured values ​​with measured value averaging, Fig. 9: a flow chart for calculating the effective tau value with time constant averaging, Fig. 10: a representation of nested tau means, Fig. 11: a second averaging schematically with adaptive adjustment and Fig. 12: a calculation of the first and second order difference quotients.

[0049] Fig. 1 shows in a functional block diagram the determination of an insulation resistance R_F1, R_F2 in an ungrounded power supply system 2 according to the state of the art.

[0050] The ungrounded power supply system 2 is designed here as an on-board power supply system of an electric vehicle and essentially consists of the two active conductors HV+ and HV-, via which a DC voltage source U_HV supplies the load R_L with power. In addition to the insulation resistances R_F1, R_F2 to be determined, the ungrounded power supply system 2 is characterized by the (natural) system leakage capacitances C_F1, C_F2, which form between the respective active conductors HV+, HV- and earth 4 and are shown here as lumped components. Y capacitors C_Y, which serve to suppress (common-mode) interference, act between the load R_L and earth 4.

[0051] To monitor the insulation resistances R_F1, R_F2, an insulation monitoring device (IMD) 5 is installed, which has a measuring pulse generator 6 which feeds a measuring voltage U 0 between one of the active conductors HV+, HV- and earth 4 into the unearthed power supply system 2 via a coupling branch with coupling resistors R_C1, R_C2 and measuring resistors R_M1, R_M2. The measuring voltage U 0 is composed of chronologically successive rectangular measuring pulses. A measured voltage U m is recorded at each of the measuring resistors R_M1, R_M2, which is converted in an analog-to-digital converter 8 (ADC) by sampling at a sampling rate f S into a sequence of time-discrete input voltage measured values ​​U i, which is fed to a downstream digital signal processing unit 10 for determining the insulation resistances R_F1, R_F2.

[0052] The ungrounded power supply system 2 and the insulation monitoring device 5 thus represent the application environment for the inventive method 30, 40 for rapid insulation resistance measurement in the first and second variants.

[0053] In the Fig. 2A und 2B is shown an equivalent circuit diagram for the charging / discharging of a capacitor C via a resistor R. In the present analysis, the capacitor C can be considered as a parallel circuit consisting of the system leakage capacitances C_F1 and C_F2 and the Y-capacitors C_Y from Fig. 1 and is charged to a stationary final value Vstat (full charge voltage, source voltage).

[0054] The Fig. 3A and Fig. 3B show the changes that occur during charging and discharging of the capacitor according to the Fig. 2A und 2B the time course of the capacitor (charging / discharging) voltages V(t) in continuous time representation.

[0055] The curve follows an exponential function, asymptotically approaching the source voltage Vstat or the value zero. The capacitor voltages V(t)=V1, V2, V3, Vt associated with the times t=t1, t2, t3, Tt are shown.

[0056] To illustrate the different charging rates, i.e., the temporal change (differential quotient) of the capacitor voltage V(t), in a transient phase and a saturation phase, two additional tangents, ke (transient phase) and ks (saturation phase), are plotted. In a discrete-time representation, these temporal derivatives correspond to the first-order differential quotients.

[0057] Fig. 4 shows the first and second order differential quotients V'(t), V"(t) (first and second derivatives) of the voltage curve of the capacitor voltage V(t) according to Fig. 3A .It can be seen that the first and second order differential quotients V'(t), V''(t) again exhibit an exponential course and have opposite signs.

[0058] Derived from the representation of the differential quotients V'(t), V"(t) in Fig. 4 shows the Fig. 5 the quotient V'(t) / V"(t) of the first-order differential quotient V'(t) divided by the second-order differential quotient V"(t). This quotient V'(t) / V''(t) corresponds to the negative time constant -tau V ′ t V " t = − RC = − tau

[0059] Fig. 6 shows a flow chart of the method 40 according to the invention with specification 55 of a target state of charge r (first variant) within the method 15 for determining the insulation resistance.

[0060] Based on the time-continuous course of the measured voltage U m, a sequence of time-discrete output voltage measured values ​​V i is formed and stored in block 60.

[0061] Fig. 8 describes the process steps required in block 60 for forming and storing the output voltage measured values ​​Vi in a flow chart.

[0062] By sampling 42 the curve of the measured voltage U m with a sampling frequency f S by means of an analog-to-digital converter, a sequence of time-discrete input voltage measured values ​​U i is generated for the subsequent digital signal processing steps.

[0063] The calculation of time-discrete output voltage measured values ​​V i from the time-discrete input voltage measured values ​​U i is carried out by a two-stage measured value averaging 44, 48 with a first averaging 44 and a second averaging 48 and a digital low-pass filtering 46 carried out between the first averaging 44 and the second averaging 48.

[0064] During the first averaging step 44, a linear temporal average is calculated for consecutive, non-overlapping blocks each comprising a number N of time-discrete input voltage measured values ​​U i , so that a sequence of decimated voltage measured values ​​X i appears as the output signal of the first averaging step 44. The number N of input voltage measured values ​​U i to be combined into a block can be preset but remains constant throughout the process.

[0065] The subsequent digital low-pass filtering 46 of the decimated voltage measurement values ​​X i calculates a sequence of filtered voltage measurement values ​​Y i.

[0066] In a second averaging step 48, analogous to the first averaging step 44, consecutive blocks with a number M of the filtered voltage measurement values ​​Y i are initially formed without overlap. A linear temporal average is then calculated for each block, resulting in the sequence of time-discrete output voltage measurement values ​​V i .

[0067] However, in contrast to the first averaging 44, in the second averaging 48 the number M of filtered voltage measured values ​​Y i to be summarized is adaptively adapted to the time behavior of the time-discrete output voltage measured values ​​V i.

[0068] This adaptive adjustment takes into account the temporal change (rate of change) of the time-discrete output voltage measured values ​​V i . The value of the second-order difference quotient V" i is preferably used as a criterion for the temporal change.

[0069] By means of a first control 49, the result of a calculation of the second-order difference quotient V" i is fed back and compared with a permissible first value range, which is specified, for example, by the limits [0.5, 2]. The number M of filtered voltage measured values ​​Y i to be summarized is set by this first control 49 such that the second-order difference quotient V" i lies within the permissible first value range and thus it can be assumed that the time-discrete output voltage measured values ​​V i correctly reflect the measured voltage curve U m.

[0070] A rapid temporal change in the time-discrete output voltage measured values ​​V i can thus be taken into account by a smaller number M of filtered voltage measured values ​​Y i used for the respective (block) averaging than would be necessary for a slow temporal change in the time-discrete output voltage measured values ​​V i. Instead of calculating a few averages over large block lengths with many filtered voltage measured values ​​Y i (with a slow temporal change), (block) averaging is carried out over small block lengths with a few filtered voltage measured values ​​Y i (with a rapid temporal change) in order to map the measured voltage U m as accurately as possible with the time-discrete output voltage measured values ​​V i and as efficiently as possible in terms of computational effort and storage capacity 47.

[0071] Clarified in detail Fig. 11 The second averaging step 48 schematically illustrates an adaptive adjustment of the number M of filtered voltage measurement values ​​Y i to be included in the (block) averaging. In this representation, the filtered (time-discrete) voltage measurement values ​​Y i are interpolated for simplification by a (fictitious) underlying continuous-time filtered measurement signal Y(t). The sequence of time-discrete output voltage measurement values ​​V i results as the output variable of the second averaging step 48 with the first control step 49.

[0072] It can be seen that within the calculation period T c in the case of rapid signal change (steep rise of the curve), a smaller number M of filtered voltage measurement values ​​Y i (corresponds to a short block length for calculating V 1 ) is included in the block-wise calculation of the respective (block) mean value than in the case of slow signal change (flat curve and longer block lengths for V 2 to V i ).

[0073] Fig. 12 shows the calculation of the first-order difference quotients V' i and second-order V" i . For time-discrete signals, the following results for the three consecutive time-discrete output voltage measured values ​​V i ={V1, V2, V3} with Δ V 1 = V 2 − V 1 , Δ V 2 = V 3 − V 2 and V ′ 1 = Δ V 1 / Δ T , V ′ 2 = Δ V 2 / Δ T as well as V " 1 = V ′ 2 − V ′ 1 Δ T the time constant tau 1 to tau 1 = − V ′ 1 V " 1 tau 1 = − Δ V 1 Δ V 2 − Δ V 1 ∗ Δ T = − V 2 − V 1 V 3 − V 2 − V 2 − V 1 ∗ ΔT

[0074] Alternatively, instead of the first-order difference quotient for the value pair {V1, V2} in the numerator of the negative quotient, the first-order difference quotient for the value pair {V2, V3} or the mean of both value pairs according to tau 1 = − Δ V 2 + Δ V 1 2 Δ V 2 − Δ V 1 ∗ Δ T = − V 3 − V 1 / 2 V 3 − V 2 − V 2 − V 1 ∗ ΔT be used.

[0075] Returning to Fig. 6 On the basis of the processed time-discrete output voltage measured values ​​V i , time constants tau i are calculated in blocks 50, 52, from which an effective tau value tau_eff is then calculated in block 54.

[0076] Fig. 9 describes the process steps required in blocks 50, 52, 54 with time constant averaging.

[0077] First, the time constant tau i is calculated as a negative quotient of the first-order difference quotient V' i and the second-order difference quotient V" i of successive time-discrete output voltage measured values ​​V i as described above.

[0078] This continuous calculation of the first-order difference quotients V' i and second-order V" i as well as the quotient formation V' i / V" i extends over a calculation period T c ( Fig. 5 ) within a transient phase of the rectangular measurement pulse. The calculation period T c preferably extends from the end of the transient process of the digital low-pass filter 46 to the beginning of the saturation phase of the capacitance charging.

[0079] After calculating 50 the sequence of time constants tau i , a calculation 54 of the effective tau value tau_eff is carried out by means of continuous calculation 52 of a nested tau mean value tau_avg k and a second-order tau difference quotient tau" k from three nested time constants tau i .

[0080] In addition, a second control 53 is executed, which adapts the number M of filtered voltage measured values ​​Y i to be included in the second averaging 48 to the temporal progression of the nested tau averages tau_avg k . In principle, the second control 53 is based on the same mechanism as the first control 49, but uses the temporal change of the tau averages tau_avg k as the comparison variable instead of the time-discrete output voltage measured values ​​V i . By feeding back the second-order tau difference quotient tau" k and comparing it with a permissible second value range, the number M is set such that the second-order tau difference quotient tau" k lies within the permissible second value range.

[0081] Fig. 10 shows a representation of the nested tau-averages tau_avg k . From the previous calculation 50, an array with, for example, 12 time constants tau i with indices 0 to 11 is available. From this array of 12 time constants tau i , K=4 nested tau-averages tau_avg k are formed, each comprising three time constants tau i . In this example, a first nested tau-average tau_avg 1 is formed from the time constants tau i with indices 0, 4, and 8, a second nested tau-average tau_avg 2 is formed from the time constants tau i with indices 1, 5, and 9, and so on.

[0082] From these groups of three time constants tau i, in addition to the tau mean value tau_avg k, a second-order tau difference quotient tau" k is also calculated, which serves in the second control 53 as an adjustment criterion for adjusting the number M in the second averaging 48.

[0083] The calculation of the second-order tau difference quotient tau" k is based on a calculation rule analogous to the calculation of the second-order difference quotient V" i of the time-discrete output voltage measured values ​​V i described above.

[0084] Subsequently, a linear averaging is performed over a number K of the nested tau averages tau_avg k to determine the effective tau value tau_eff as the relevant time constant for the calculation 56 ( Fig. 6 ) of a target time Tt.

[0085] If the effective tau value tau_eff is known, the Fig. 6 after specifying 55 the target state of charge r, calculating the target time Tt.

[0086] With the state of charge r=Vt / Vstat as the ratio of a target charging voltage Vt reached in this target charging state to a stationary final value Vstat (full charging voltage) of the capacitor voltage, it follows from Vt = Vstat ∗ 1 − e − Tt / tau _ eff r = Vt / Vstat = 1 − e − Tt / tau _ eff Tt = tau _ eff ∗ ln 1 − r

[0087] The first waiting time dTr is then the difference between the target time Tt and the current time T3 (Block 57) dTr = Tt − T 3

[0088] Finally, in block 58, a check is performed to determine whether the determined first waiting time dtr is less than a predefined quick start time Ts. If the first waiting time dtr is less than a predefined quick start time Ts, i.e., the quick start requirement is met, a safe start signal ss is output; otherwise, a non-safe start signal ns is output as a warning.

[0089] Fig. 7 shows a flow chart of the method according to the invention with specification 35 of a target charging speed kt (second variant) within the method 15 for determining the insulation resistance.

[0090] As in the first variant after Fig. 6In block 60, the measured voltage Um is first processed and stored in the form of a sequence of time-discrete output voltage measured values ​​V i . The calculation 50, 52 of the time constant tau i and the calculation 54 of the effective tau value tau_eff also correspond to the method steps of the first variant.

[0091] The difference to the first variant is that instead of the target state of charge of 55, r, a target charging speed of 35, kt is specified.

[0092] The target charging speed kt corresponds to the change of the capacitor voltage over time according to V ′ t = dVt / dt V ′ t = − Vstat / tau _ eff ∗ e − Tt / tau _ eff

[0093] The same applies to the already calculated and stored voltage values ​​V2 and V'2 at the time T2 t=T2 V ′ 2 = − Vstat / tau _ eff ∗ e − T 2 / tau _ eff

[0094] This means V ′ t / V ′ 2 = e T 2 − Tt / tau _ eff and with V ′ t = kt T 2 − Tt = tau _ eff ∗ ln kt / V ′ 2 = dTr as second waiting time dTr.

[0095] Here, too, a check is carried out in block 38 as to whether this second waiting time dTr, starting from the T2 time T2, is less than a predetermined quick start time (Ts) and thus fulfills the quick start requirement, so that a safe start signal ss can be output.

Claims

1. A method (40) for quickly measuring an insulation resistance for the application in a method (15) for determining the insulation resistance (R_F1, R_F2) according to a pulse measuring method in an ungrounded power supply system (2), a measuring voltage (U0) compiled of temporally consecutive square measuring pulses being applied between an active conductor (HV+, HV-) of the ungrounded power supply system (2) and ground (4) by means of a measuring pulse generator (6) via a coupling branch having a coupling resistance (R_C1, R_C2) and a measuring resistance (R_M1, R_M2) and a continuous-time curve of a voltage (Um) measured via the measuring resistance (R_M1, R_M2) being captured, the method comprising the following steps: forming and storing a sequence of time-discrete output-voltage measured values (Vi) from the curve of the measured voltage (Um), calculating time constants (50, taui) as negative quotient from a derivative of the first order (V'i) and a derivative of the second order (V"i) of time-discrete output-voltage measured values (Vi = V1, V2, V3) stored at temporally directly consecutive points in time (T1, T2, T3) in a calculating period (Tc) within a settling phase of the square measuring pulse, calculating an effective tau value (54, tau_eff) via time constant averaging, characterized by indicating (55) a target charging state (r) of the network capacities (C_F1, C_F2) available in the ungrounded power supply system, calculating a target point in time (Tt) at which the network capacities (C_F1, C_F2) will have reached the target charging state (r) from the target charging state (r) and the effective tau value (54, tau-eff), calculating a first wait time (dTr) starting from the current point in time (T3) as the difference between the target point in time (Tt) and the current point in time (T3), outputting a safe-to-start signal (ss) should the first wait time (dTr) be less than an indicated quick-start time (Ts), otherwise outputting a not-safe-to-start signal (ns).

2. The method according to claim 1, characterized in that the time-discrete output-voltage measured values (Vi) are formed by generating a sequence of time-discrete input-voltage measured values (Ui) by sampling (42) the curve of the measured voltage (Um) with a pre-specified sampling rate, by calculating the time-discrete output-voltage measured values (Vi) from the time-discrete input-voltage measured values (Ui) via measured-value averaging (44, 48) via sampling-rate reduction, by calculating filtered voltage measured values (Yi) via digital low-pass filtering (46) of decimated voltage measured values (Xi).

3. The method according to claim 2, characterized in that the measured-value averaging comprises a first averaging (44), the decimated voltage measured values (Xi) each being formed consecutively without overlap via a number N of the time-discrete input-voltage measured values (Ui).

4. The method according to claim 2 or 3, characterized in that the measured-value averaging comprises a second averaging (48), the time-discrete output-voltage measured values (Vi) each being formed consecutively without overlap via a number M of the filtered voltage measured values (Yi) and the number M being adapted to the temporal behavior of the time-discrete output-voltage measured values (Vi).

5. The method according to claim 4, characterized in that the adaption takes place via a first control (49), which sets the number M as a function of the derivative of the second order (V"i) of the time-discrete output-voltage measured values (Vi) in such a manner that the derivative of the second order (V"i) of the time-discrete output-voltage measured values (Vi) is within an admissible first value range.

6. The method according to claim 4 or 5, characterized in that an interleaved tau average (tau_avgk) and a tau derivative of the second order (tau"k) are each calculated in the time-constant averaging for calculating the effective tau value (54, tau_eff) continuously from three time constants (taui), which are summarized in an interleaved manner, a second control (53) taking place which sets the number M as a function of the tau derivative of the second order (tau"k) in such a manner that the tau derivative of the second order (tau"k) is within an admissible second value range, and subsequently an averaging takes place via a number K of the interleaved tau averages (tau_avgk) for calculating the effective tau value (tau_eff).

7. The method according to any one of the claims 1 to 6, characterized in that a stationary final value (Vstat) of the capacitor voltage is calculated from one of the stored, time-discrete voltage measured values (Vi = V1, V2, V3), from the correspondingly assigned point in time (t1, t2, t3) and from the effective tau value (tau_eff).

8. A method (30) for quickly measuring insulation resistances for the application in a method (15) for determining the insulation resistance (R_F1, R_F2) according to a pulse measuring method in an ungrounded power supply system (2), a measuring voltage (U0) compiled of temporally consecutive square measuring pulses being applied between an active conductor (HV+, HV-) of the ungrounded power supply system (2) and ground (4) by means of a measuring pulse generator (6) via a coupling branch having a coupling resistance (R_C1, R_C2) and a measuring resistance (R_M1, R_M2) and a continuous-time curve of a voltage (Um) measured via the measuring resistance (R_M1, R_M2) being captured, the method comprising the following steps: forming and storing a sequence of time-discrete output-voltage measured values (Vi) from the curve of the measured voltage (Um), calculating time constants (50, taui) as negative quotient from a derivative of the first order (V'i) and a derivative of the second order (V"i) of time-discrete output-voltage measured values (Vi = V1, V2, V3) stored at temporally directly consecutive points in time (T1, T2, T3) in a calculating period (Tc) within a settling phase of the square measuring pulse, calculating an effective tau value (54, tau_eff) via time constant averaging, characterized by indicating (35) a target charging rate (kt), which is to be achieved in a target point in time (Tt) at the network capacities (C_F1, C_F2) available in the ungrounded power supply system, calculating a second wait time (dTv) starting from the T2 point in time (T2) as the difference between the target point in time (Tt) and the T2 point in time (T2) from the effective tau value (54, tau_eff) and starting from the quotient from the target charging rate (kt) and the determined derivative of the first order (V'2) to the T2 point in time (T2), outputting a safe-to-start signal (ss) should the second wait time be less than a pre-specified quick-start time (Ts), otherwise outputting a not-safe-to-start signal (ns).

9. The method according to claim 8, characterized in that the time-discrete output-voltage measured values (Vi) are formed by generating a sequence of time-discrete input-voltage measured values (Ui) by sampling (42) the curve of the measured voltage (Um) with a pre-specified sampling rate, by calculating the time-discrete output-voltage measured values (Vi) from the time-discrete input-voltage measured values (Ui) via measured-value averaging (44, 48) via sampling-rate limitation, by calculating filtered voltage measured values (Yi) via digital low-pass filtering (46) of decimated voltage measured values (Xi).

10. The method according to claim 2, characterized in that the measured-value averaging comprises a first averaging (44), the decimated voltage measured values (Xi) each being formed consecutively without overlap via a number N of the time-discrete input-voltage measured values (Ui).

11. The method according to claim 9 or 10, characterized in that the measured-value averaging comprises a second averaging (48), the time-discrete output-voltage measured values (Vi) each being formed consecutively without overlap via a number M of the filtered voltage measured values (Yi) and the number M being adapted to the temporal behavior of the time-discrete output-voltage measured values (Vi).

12. The method according to claim 11, characterized in that the adaption takes place via a first control (49), which sets the number M as a function of the derivative of the second order (V"i) of the time-discrete output-voltage measured values (Vi) in such a manner that the derivative of the second order (V"i) of the time-discrete output-voltage measured value (Vi) is within an admissible first value range.

13. The method according to claim 11 or 12, characterized in that an interleaved tau average (tau_avgk) and a tau derivative of the second order (tau"k) are calculated in the time-constant averaging for calculating the effective tau value (54, tau_eff) continuously from three time constants (taui) each, which are summarized in an interleaved manner, a second control (53) taking place which sets the number M as a function of the tau derivative of the second order (tau"k) in such a manner that the tau derivative of the second order (tau"k) is within an admissible second value range, and subsequently an averaging takes place via a number K of the interleaved tau averages (tau_avgk) for calculating the effective tau value (tau_eff).

14. The method according to any one of the claims 8 to 13, characterized in that a stationary final value (Vstat) of the capacitor voltage is calculated from one of the stored, time-discrete voltage measured values (Vi = V1, V2, V3), from the correspondingly assigned point in time (t1, t2, t3) and the effective tau value (tau_eff).